lib/stop.cpp

The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <stop_token>
#include <future>     // for std::async()
#include <thread>     // for sleep_for()
#include <syncstream> // for std::osyncstream
#include <chrono>
using namespace std::literals;  // for duration literals

auto syncOut(std::ostream& strm = std::cout) {
  return std::osyncstream{strm};
}

void task(std::stop_token st, int num)
{
  auto id = std::this_thread::get_id();
  syncOut() << "call task(" << num << ")\n";

  // register a first callback:
  std::stop_callback cb1{st, [num, id]{
    syncOut() << "- STOP1 requested in task(" << num
              << (id == std::this_thread::get_id() ?  ")\n"
                                                   :  ") in main thread\n");
  }};
  std::this_thread::sleep_for(9ms);

  // register a second callback:
  std::stop_callback cb2{st, [num, id]{
    syncOut() << "- STOP2 requested in task(" << num
              << (id == std::this_thread::get_id() ?  ")\n"
                                                   :  ") in main thread\n");
  }};
  std::this_thread::sleep_for(2ms);
}

int main()
{
  // create stop_source and stop_token:
  std::stop_source ssrc;
  std::stop_token stok{ssrc.get_token()};

  // register callback:
  std::stop_callback cb{stok, []{
    syncOut() << "- STOP requested in main()\n" << std::flush;
  }};

  // in the background call task() a bunch of times:
  auto fut = std::async([stok] {
                          for (int num = 1; num < 10; ++num) {
                            task(stok, num);
                          }
                        });
  
  // after a while, request stop:
  std::this_thread::sleep_for(120ms);
  ssrc.request_stop();
}